Protecting public health and water quality is the goal of an onsite wastewater treatment system. Many treatment technologies are available to meet this goal. The selection of an appropriate technology is dictated by site and soil conditions. Mound systems are one type of onsite treatment technology.
Conventional septic tank-absorption field systems may not be suitable for onsite wastewater treatment based on the site conditions and soil characteristics. Current Ohio regulations require a minimum of 4 feet of unsaturated and permeable soil for onsite wastewater treatment and disposal. Based on data from county soil surveys, only 6.4% of Ohio land area presents suitable soil characteristics for conventional systems. Mound systems can be used to overcome the natural limitations for sites that do not meet the requirements and to achieve the goals of protecting water quality and public health. Figure 1 demonstrates the cross section of conventional soil absorption and the mound system in relation to ground surface and limiting conditions.
Figure 1. Cross section of conventional soil absorption unit (a) and
the mound system (b) in relation to ground surface and limiting
conditions.
(After Converse and Tyler, 1990, Wisconsin Mound Soil
Absorption System: Siting, Design and Construction Manual, University
of Wisconsin-Madison.)
Many mound systems have been installed and are operating in Ohio. The Household Sewage Rules (Chapter 3701-29, Ohio Administrative Code) contain no specific guidance for mound systems. This bulletin describes the procedures for siting, design, construction, management, and maintenance of mound systems. The goal of appropriate mound systems is to protect the water quality and public health in Ohio when applying for variance with the local health department or a permit to install from the Ohio Environmental Protection Agency.
In conjunction with this bulletin, two other bulletins should also be used to achieve a sound mound system. One bulletin is Suitability of Ohio Soils for Treating Wastewater (Bulletin 896), and the other is Mound Systems: Pressure Distribution of Wastewater—Design and Construction in Ohio (Bulletin 829).